H^MATOLCECHUS (dISTOMUM). 39 



tween the second and third anterior gut diverticula on either 

 side of the main anterior ramus for the two ovaries. 



(c) The oviducts pass backward from the ovaries, parallel 

 to the vasa deferentia, and unite posterior to the penis. The 

 common duct thus formed enters the posterior part of the geni- 

 tal atrium. The oviduct is difficult to demonstrate and it may 

 be necessary to try both fresh and stained material. 



(d) Along the margins of the animal, between the divertic- 

 ula of the gut, are rounded bodies, the vitellaria. These dis- 

 charge their products into the oviducts. Do you know what 

 they are for? 



Draw the female reproductive system. 



Study stained and mounted specimens for any points 

 which have not been found, and particularly examine the ner- 

 vous system. Look for the marginal nerve running along the 

 edge of the body, and for numerous transverse commissural 

 nerves. How many of these are there? How regular is their 

 arrangement ? ^ 



TREMATODA» 

 Trematodes are flat worms which lead a wholly parasitic 

 life, but which have retained, to a greater or less degree, those 

 organs that characterize free-living animals. Some Trematodes 

 are parasitic upon the outside (or ectoderm) of other animals, 

 and are hence called ''ectoparasites." 



HAEMATOLOECHUS (DISTOMUM). 



This form is found as a parasite in the lungs of frogs. In 

 some localities a large proportion of the frogs are infested and 

 several specimens are frequently found in one frog. The host 

 of the asexual generation of this species is not known, but in a 

 closely allied species the asexual generation lives in the pond- 



* A Polyclad, Planocera, can be obtained without difficulty from the 

 mantle chamber of Sycotypus. If Sycotypus is allowed to remain out of 

 water for some hours the Planocera usually crawl out. The form is fairly 

 satisfactory for study. 



